Preparation of hexafluorobutadiene



PREPARATION OF HEXAFLUURDBUTA'DENE William T; Miller, Ithaca, NLY;

No Drawing. Application July 13,1955 Serial No. 521,899

4-Cls. (Cl. 260-43535)- This invention relates to .a method for preparingaliin suchapplications as gasket and packing materials,- electrical insulation, chemical process equipment, as. Other uses of such lubricants, heat transfer media, etc. compounds need not be detailed here as they are now known to those skilled in the art.

The compounds produced by the method of the present. invention are useful as monomers in the preparation of polymeric materials or as intermediates in producing such monomers.

The compounds produced by this method and the polymers produced therefrom are useful as lubricants, heat transfer media, plastics, solvents and as plasticizers for fluorine-containing polymers of high molecular weight. This is of especial value since such plasticizers or solvents-are notiaifected by reactive chemical agents.

One of the objects of this. invention is to provide a method for preparing aliphatic compounds completely substituted with chlorine and fluorine or with fluorine.

Still another object is to provide an economical method fortproducing in high yield relatively long chain fluoroand. fluorochloro carbon compounds.

A further-object of the invention is to provide a method of preparing completely substituted fluorochloro or fluoro olefins useful as monomers in preparing high molecular weight plastic materials.

Other objects and advantages will become apparent fromsthe accompanying description and disclosure.

In general,-the foregoing objects are achieved by reacting elemental fluorine with at least one olefin of the formula CR R CR R; where each of the substituents R R R andR, is selected from the group consisting of chlorine, fluorine, a perfluoro group and a perfluoro chloro-group, preferably acyclic groups. The reactant olefins are limited to those in which at leastone of the R substituents contains fluorine and at least three of the 2,894,042 Patented July 7, 1959 10". C. or. less. in -.order to producea satisfactory yield.

of the dimer, particularly for. low molecular weightcompounds having 2,.3 or 4 carbon atoms, and these are my.

preferred group, especially when the twoR substituents on one of thecarbon atoms of the ethylene arefluorine and/or chlorine. However, in the case of higher molecular weight compounds temperatures up :to about 50". C. are useful. Also it isnotable that some ethylene reactants which react sluggishly when treated alone will react more easily when condensed with a relatively reactive olefin to form a mixed condensation product. Examples of these and other reactions which appear hereinafter will serve to indicate and explain the scope of reaction products are formed'generally by end-to-end condensationwith the simultaneous addition of fluorine in the 1,4-positions of the butane product thus:

The .products :formedfin this manner have the general formula .CFR R 'CR R -GR R CFR R where the R substituents are as definedin the preceding paragraph.

The four. carbon atoms of the ethylenic double bonds of two molecules which react in thisway are treated herein as a butane even though they may bepart of a ring-structure or structures: The addition of fluorine on the end 1 valences .of the reactant olefin groups serves to prevent Other. substituted" the formationof higher compounds. butane compoundsEare-also produced by side reactions in which fluorine participatesn Such reactions mayv be the result of fluorine substitution, or the addition of the ele ments: of chlorine fluoride which may be formed in the The mechanism of fluorine substitution. .or otherwise. these side reactions is uncertain;

Whenmore than one double bond is present in the olefinic reactant, for example a butadiene, products hav ing longenchains than a dimer. may be formed in the reaction. This occurs because the fluorine in the usual case will add. only on the carbon atoms of the olefinic groupswhich participated in the initial condensation re-v action. Accordingly, unsaturated olefinic groups of the dimer are still available forxfurther. reaction with the original reactant or .With'unsaturated condensation products already formed.

The olefinsare prepared in accordance with this inven tion and these olefinsare usedin the. production of higher molecular weight compounds. When at least: one of the R substituents on theiethylenic reactant is chlorine the resultant butane with chlorine .on adjacentcarbon atoms is dechlorinated relatively easily without affecting the fluorine in the molecule. For. exarnple, a preferred'olefinic compound is symmetrical .difluorodichloroethylene,=

CFCl=CFCl.. When this compound is treated: with fluorine at a temperature of less than 10 C., 1,2,3,4-tetrachloroperfluorobutane, CF ClCFClCFCl-CF Cl, is produced; The tetrachlorobutaneis then, according to this invention, dechlorinated'to yield a very valuable monomer hexafluorobutadiene-1,3 ,CF =CFCF=CF This diolefin is reacted with'fluorine to produce compounds ofleight, twelve, sixteen,'etc., carbon atoms, ac-

3 cording to the mechanism postulated in the preceding paragraph.

The dehalogenation reaction of this invention is carried out at a temperature between about 50, C. and about 250 C., preferably between about 100 C. and about 200 C. in the presence of a metal dehalogenating agent, such as zinc, in finely divided form. An alcohol is employed as a solvent or diluent during dehalogenation. The reaction may be carried out at atmospheric or superatmospheric pressure without departing from the scope of this invention.

The following examples are illustrative of the method:

' EXAMPLE 1 In a number of experiments, the following procedure was used: About 1120 grams of sym-difluorodichloroethylene (CClF=CClF) having a boiling point of about 20 to 23 C. was placed in a vessel having an inlet arm. A roll of copper gauze was then pushed into the inlet arm until it was just at the surface of the body of liquid monomer. The copper gauze, a stopper and an inlet tube were then inserted in the inlet arm making certain that the arm was sealed to the atmosphere.

. A Dry Ice-acetone mixture was packed around the reaction vessel to cool it. The stin'er was then started in order to circulate the liquid reactant, and the vessel was flushed with nitrogen. Thereafter, fluorine was passed into the vessel at a rate approximately equal to the rate at which it was absorbed. The reaction was halted when a strong test for fluorine was obtained at the vessel outlet. In the series of experiments, the average yield was between 400 and 500 grams of 1,2,3,4-tetrachloroperfluorobutane, CF ClCFClCFClCF Cl. This compound may be distilled from the reaction mixture at a temperature between 60 and 70 C. at 75 mm. of pressure. The yield is about 30 to 40 percent based on the theoretical amount obtainable.

In a typical reaction other perchlorofluorobutanes are also obtained and it has been found that the yield of such compounds varies with temperature. In one run at the temperature of the Dry Ice-acetone bath the y eld of C Cl F was 30.0 percent while a 3.8 percent yield of C C1 F and a 2.1 percent yield of C Cl F were obtained.

A valuable product is obtained by dechlorinating the tetrachloro compound to yield hexafluorobutadiene-1,3. In a typical procedure for the dechlorination, 556 grams of zinc dust were suspended in 1.5 liters of absolute alcohol to which one kilogram of 1,2,3,4-tetrachloroperfluorobutane was added over a period of time. By adjusting the rate atwhich distillate was removed, a fairly constant reflux temperature of about 7 to 9 C. (uncorrected) was maintained and the hexafluorobutadiene was distilled continuously from the reaction flask. Employing the quantities of zinc, alcohol and butane indicated above, a yield of about 503 grams of hexafluorobutadiene- 1,3 was obtained. This is a yield of about 95 percent of theoretical dechlorination.

-The properties of 1,2,3,4-tetraohlorohexafluorobutanev are as follows: boiling point 134.1 C. (corrected to 760 mm. Hg.); refraction index 21 1.3853; density D 1.7812. The analysis as determined on a typical sample was 15.72 percent carbon and 37.45percent fluorine (theoretical 15.8 and '37 .5 percent, respectively). The molecular weight as determined on the same sample was 305 (theoretical 304).

The properties of C Cl F are as follows: boilingpoint 90-92 (78 mm.); r1 1l4203;'D' 1.7961; The fluorine analysis was 29.5 (theoretical 29.7 percent).

The properties of C CI F are as follows: boiling point 125128 C. (76 mm.); n 1.457. The fluorine analysis was 21.35 percent, the chlorine analysis 63.4 percent average (theoretical 22.63 and 63.2 percent, respectively).

EXAMPLE 2 The fluorination procedure described in Example 1 was present '4 also carried out with SYIIl-diflllOlOdiChlOIOEiihYlCHB at a temperature of approximately 0 C. by using crushed ice as coolant. From the fluorination a 6.5 mol percent yield of C Cl F was obtained together with 7.2 mol percent of C Cl F and 4.4 mol percent C Cl F Relatively large amounts of the fluorine addition product of the ethylene and various fluorine-substitution products are also obtained at this temperature.

EXAMPLE 3 The same reaction between CCl=CClF was carried out using a Dry Ice-acetone bath as coolant which gives a temperature of about C. The yield of 1,2,3,4- tetrachloroperfluorobutane was about 49 percent.

Examples 2 and 3 illustrate the effect of temperature on the reaction. The yield of the dimer is markedly decreased as the temperature of the reaction is increased about 10 C. while the yield of fluorine addition and substitution products is increased at the higher temperatures.

In order to dechlorinate the 1,2,3,4-tetrachloroperfluorobutane produced as above, 99.7 grams of the compound were added in small amounts to a suspension of 55 grams of CF. zinc dust in 200 cc. of butyl carbitol. The reaction vessel was maintained at an elevated temperature by means of an oil bath heated to about 200 C. The reaction mixture was maintained at reflux temperatures and the reaction proceeded smoothly as the tetrachlorobutane was added. This procedure was repeated with a second sample of the tetrachlorobutane weighing 102 grams, and about 60 grams of zinc dust were used suspended in cc. of butyl carbitol. The products of the two experiments were combined and distilled. The distillation yielded about 35 grams of hexafluorobutadiene-1,3.. This is a yield of about 64 percent in the dechlorination.

' EXAMPLE 4 A solution of 408 grams of syrn-difluorodichloroethylene dissolved in 108.5 grams of C CI F (1,1,2-trichloroperfluoroethylene), was reacted with fluorine as already described using Dry Ice as coolant. The reaction product was fractionally distilled and 76.7 grams of the tetrachloroperfluorobutane were collected at 64 to 66 C. at a pressure of 75 mm.

The tetrachloroperfluorobutane was dechlorinated with zinc dust suspended in dry dioxane to yeld the compound CF Cl-CF=CF-CF CI as well as a small amount of hexafluorobutadiene. The monoolefinic butene compound has a boiling point of 65.5 to 65.7 C. at 744 mm. and its molecular weight was determined at 233 (theoretical 233). The chlorine content was determined as 33.2 percent (theoretical 32.8 percent).

EXAMPLE 5 Trifluorochloroethylene was reacted with fluorine with Dry Ice-acetone cooling to yield the compound C F Cl with the isomer CF --CFCl-CFCl-CF 2,3-dichloroperfluorobutane predominating. This isomer has a boiling point of 64 C. and a refractive index 11 1.3109. The molecular weight was determined as 270 (theoretical 271).

This 2,3-dichloroperfluorobutane was dechlorinated with zinc to yield perfluorobutene-Z which has the following properties: freezing point 134 to -l36 C.; boiling point 1.2 C. (764.3 mm.); density D 1.001. The grgglgcular weight was determined as 201 (theoretical Isomers of 2,3-dichloroperfluorobutane having the chlorine atoms in the 1,3 positions and in the 1,4 positions are also formed in the condensation reaction. The L4 dichloro isomer may also be prepared by fluorinating the compound CF ClCF=CFCF Cl (prepared as in Example 4) with elemental fluorine. The latter isomer has a boiling point of 64 C.

The 1,2-dichlno isomer, as prepared by chlorinating perfiuorobutene-l, has a boiling point of 64" C. and a freezing point of 28-9 C. The-observed carbon'rcom tent was 18.2 percent (theoretical 17.7) and the ob'- served molecular weight was 273 (theoretical 271)..

EXAMPLE 6 At about 0 to C., 181.3 grams of CF -CCI=CCI was reacted with about 0.7 mole of fluorine diluted with nitrogen to obtain a 16.9 mole percentyield of CGCIGFQ.

EXAMPLE7 The compound CF CCl=CCl (240 grams) was diluted with C Cl F (201.5 grams) and thereafter treated with 1.0 mole of fluorine diluted with nitrogen at a temperature of about 05 C. A yield of 14.7 mol percent C CI F was obtained.

This compound C CI F as .preparedby. the. methods of Examples 6 and 7 has the following properties: boil: ing point 115 C. (20 mm.); n 1.4387; densitytD}; 1.9415. The chlorine content was determined as 49.1 percent (theoretical 48.7); the fluorine content was determined as 33.2 percent (theoretical 34.8); the molecular weight was determined as 429 (theoretical 437). The probable structure of this compound is:

CFg CF 3 CFClz-CCl-CC1OFC1 EXAMPLE .8

The compound 2-chloroperfluoropropene was reacted with fluorine at a temperature of about --75 C. The compound C Cl F obtained with "a yield 'of T about 57 percent, had the structural formula CFa CF3 CF3C C1.O Cl-C F3. This compound was separated by distillation at 114 to 115.5 C. at 735 mm. Hg. The molecular weight of the compound was determined as 379 (theoretical 371) and the chlorine content was determined at 19.18 percent'(theoretical 19.12). After recrystallization from ethylalcohol' the product was found to sublime. at a temperature be-; tween and C. and'the melting .point: was. deter-1 mined in a sealed tube as 91.5 to 93.0- C;

This compound was dechlorinated .to. fiorm C F with J a yield of 85 percent. A Zinccopper couple,tprepared by maintaining zinc :dust in contactwith'a solution of copper sulfate, was used for the dechlorination-with di-i oxane as solvent. The dechlorinate'dicompound has a boiling point of 545 C. and a density D 'of 1.'6924,'- and its molecular weight after bromination'was-deter? mined as 461 (theoretical-460). The=dechlorinated com=- pound, C F has the structural formula:

C F3- =C'C F3 and may be fluorinated to yield "the. addition pnodu'ct C F which has a boiling point of 57.5-59.0". C; and a density D 1.7729.

EXAMPLE 9 I A similar reaction to that described in Examp1ei8 was carried out with Dry Ice coolant. (about .-5-2-C.). From 152.3 grams of CF -CCl=CF a total. of 32.1 .grams.

of C F Cl were recovered with a boiling range of 114 to 115.5 C. at atmospheric pressure The-molecular weight of this sample was determined as 371 (theoretical 371) and its chlorine analysis as 19.35 percent (theoretical 19.12 percent).

A sample of this compound was dechlorinated 'with a zinc-copper couple using absolute ethanol and another sample was dechlorinated under approximately the same conditions using di'oxa'ne as solvent. In each 'case' the compound C F was obtained.

EXAMPLE 10' The compound CF -CCl=CF (96.5 grams) dissolved in'53.6 grams of trichlorofluoromethane, CCl F;

was reacted with fluorine. The reaction was carried out with cooling by a Dry Ice-acetone mixture. The same reactionwas repeated under the same conditions using 100.4 gramsof CF -CCl=CF- disolved in 47.8 grams of CCl F. From the two experiments, 125.0 grams of- C F Cl were obtained.

EXAMPLE 11 About 110 grams of 1,4-dichloroperfluorobutene-Z,

CClF CF CF-CClF were reacted with fluorine in. a vesselcooled with crushed ice, the temperature being about 0 to 5 C; A yield of about 12.4 percent of.

C CI F with a boiling point of 125 to 126 C. (70 mm.) was obtained. This compound has the structural formula:

F ClC GOlF OOIFr-o F -C F-C F-G Fg-C 01F,

EXAMPLE 12 Using a Dry Ice-acetone coolant, a mixture of 107 grams of sym-dichlorodifiuoroethylene and 187 grams of 2,3-dichlorohexafluorobutene-2, CF CCl=CClCF bzoth dissolved in 107 grams of trichlorofluoromethane,

was treated with 0.5 mole of fluorine diluted about 1:1

with nitrogen-over a period of 7 hours. From the reaction mixture 53.9 grams of the mixed condensation product r CC1F2-CO1F-CCl-OO1F-CF3 were separated. This compound has a boiling point of 175.8 to 176.0 'C. at atmospheric pressure and of 108.0 to 108.2 at 100 mm; of pressure. The solidification point, determined a sealed glass tube, was between and C. The density D was 1.9016 and the refractive index 11 was 1.3861. The average chlorine content was determined as 35.3 percent (theoretical 35.1 percent); the molecular weight as determined was 421 (theoretical 404). over a wide range of temperature (75 C. to 176 C.) is noteworthy. This example illustrates the condensation of two different ethylenic molecules.

EXAMPLE 13 or maybe a mixture of both. However, it is most likely that the dominant isomer is the latter one, and this is a very valuable compound since it may be dechlorinated to yield methyl-substituted conjugated perfluorobutadiene, a valuable monomer for preparing high molecular weight plastic polymers.

EXAMPLE 14 Under essentially the same conditions as those of Example 12, a mixture of sym-dichlorodifiuoroethylene and perfiuorocyclobutene,

(I) F2-C F The fluidity of this compound were condensed together by the fluorine treatment to yield the compound,

This product has a boiling point of 104.6 to 105 C. and solidifies in a sealed glass tube between 84 and 100 C. The density D is 1.7410 and the refractive index n is 1.3294. The measured molecular weight was 336 (theoretical 333) and the chlorine content was found to be 21.2 percent (theoretical 21.3). This example illustrates the condensation of a cyclic and an acyclic compound, each containing an ethylenic double bond. In this case the substituted groups R and R in the formula CR R CR R are considered to be two difluoromethylene groups, CF on the carbon atoms of the ethylene groups with the substituents R and R joined by a common carbon to carbon bond.

EXAMPLE 15 Under essentially the same conditions used in Example 12, perfluorocyclobutene alone was treated with fluorine with the reactant dissolved in an inert solvent as described. The condensation product was isolated from the reaction mixture and it has the formula:

This compound boils at a temperature of 86.2 to 873 C. and melts at 6.75 C. Its density D is 1.7511 and its refractive index 11 is 1.295. The measured molecular weight was 366 (theoretical 362). This example illustrates the condensation of two molecules of a cycloolefin.

EXAMPLE 16 About 546 grams of hexafluorobutadiene-l,3 were treated with fluorine in a vessel cooled with a Dry Iceacetone mixture. The fluorine treatment was continued until the reaction mixture became too viscous to be circulated. The temperature was then permitted to rise to about C. with the reaction vessel cooled with crushed ice. The fluorine treatment was then continued at 0 C. with stirring until the absorption of fluorine became slow.

The reaction mixture was then distilled to obtain the following fractions: (1) 12.0 g., B.P. 8090 (750' mm.); (2) 88.1 g., 3.1. 95-102 (750 mm.); (3) 20.6 g., B.P. 30-80 (40 mm.); (4) 42.4 g., B.P. 8089 (40 mm.); (5) 20.2 g., B.P. 89 (40 mm.) to 93 at mm.); (6) 37.1 g., B.P. 93-103 (10 mm.); (7) 49.4 g., B.P. 105 to 127 (5 mm.); (8) 119.0 g. solid residue. All of the fractions were found to contain a considerable amount of unsaturation and several of the fractions were then treated separately with chlorine with light and heat and then redistilled to remove residual unsaturated ma- This example represents a typical reaction of a conjugated diolefin to yield varying amounts of higher molecular weight compounds. The results are probably due to the condensation of reactant butadiene with unsaturated product already formed and to condensation of unsaturated products. It is evident that the length of the chain does not interfere with the reaction of the double bond. This is further illustrated in Examples 17 and 18.

EXAMPLE 17 Table 2 Boiling Point Fraction Yield,

percent 102-104" C. (10 mm.) C 22 l-186C. (l0 mm.) C14 19 W225). (10 mm.) Caz 36 EXAMPLE 1s The 12-carbon atom unsaturated product of the hexafluorobutadiene thermal reaction (described in my copending application Serial No. 601,387, filed June 25, 1945, now abandoned) was treated with fluorine at a temperature of less than 0 C. to yield compounds containing 24 and 36 carbon atoms. For example, from 303 grams of the trimer, 132 grams, roughly a 40 percent yield, of the C and C compounds were obtained boiling in the range 140 to 235 C. at 10 mm. A residue of 49.4 grams, about 15 percent, was obtained and consisted essentially of still higher molecular weight condensation products.

The fractions obtained in Examples 12, 13 and 14 vary in viscosity according to their molecular weight and the higher molecular weight fractions are particularly valuable as lubricants. Any unsaturation in these compounds may be destroyed by treating them with cobalt trifluoride or chlorine trifluoride (ClF at an elevated temperature.

It is apparent from the foregoing description that a wide variety of compounds may be prepared in accordance 'with this invention. Using the procedures described in detail in the examples other fluorine-containing butanes, butenes, and butadienes may also be prepared. For example, the reaction of tetrafluoroethylene with fluorine yields n-decafluorobutane, C F The reactions of asymmetrical dichlorodifluoroethylene and of trichlorofluoroethylene yield particularly valuable butanes which may be dechlorinated to give butene or butadiene compounds useful in the preparation of higher molecular weight polymers. For example, treatment of the trichlorofluoroethylene proceeds according to the following reaction:

The butane CF, ClCCl -CC1 CF Cl has a boiling point of -126 C. (76 mm.). The dechlorinated product, CF =CCl-CCl=CF has a boiling point of 67-70 C. The chlorine-containing conjugated butadienes may be reacted in a manner similar to hexafluorobutadiene-1,3 to yield higher molecular weight products. The following reaction is also of considerable interest since it yields a conjugated butadiene with methyl substituents by dechlorination:

F1 20 F,-o o1= oro1 or, CF; Zn F30 or. oF,c1oc1-oo1cF=o1 0Fi=oo=o1 The methyl substituted butadienes may also be employed in preparing higher molecular weight compounds. The reaction of perfluorobutene-l with fluorine yields perfluorooctane. The reactan olefin may also have perfluoro or perfluorochloro cyclic substituents, for example the perfluorophenyl radical or perfluorochlorocyclohexyl radical. Generally, treatment of a mixture of two or more olefins with fluorine in accordance with this invention yields all of the possible condensed products including those in which molecules of each of the reactants have combined. An important co-condensation is the following:

This butane may also be dechlorinated to yield the conjugated butadiene CF =CClCF=CF- As noted hereinbefore the temperature of the reaction has a considerable effect on the relative amounts of the different products produced. Thus, at the lower temperatures, the production of the condensation product is favored while at higher temperatures, of the order of C. and more for example, fluorine addition and substitution products tend to increase with relatively lower yields of the dimer. However, some of the higher molecular weight olefins, such as octenes, react with fluorine to produce compounds which are too viscous below 10 C. to be circulated and these require higher temperatures, up to about 50 C. Perfluoroolefins are more satisfactory than chloroperfluoroolefins for reaction at temperatures above 10 by the process of this invention because by-products due to the transfer of chlorine cannot arise.

The use of a solvent for the reaction with fluorine is often effective for the purpose of keeping the products fluid at the low temperatures employed. Of course, it is required that any solvent used be inert to fluorine and for this reason the saturated, lower molecular weight non-hydrogenous fluorocarbons and chlorofluorocarbons, such as the freons, are preferred as a class. These compounds are not only resistant to fluorine but for the most part are also fluid at the low temperatures required for carrying out my method. The solvent is also effective in regulating the rate of reaction. Dilution of the fluorine with an inert gas such as nitrogen is also helpful in moderating the reaction.

It will be noted that the compounds produced by the present method are formed by head-to-hea or tailto-tail condensation. Isomers of these compounds may also be formed in the reaction by head-to-tail condensation, but in the usual case one isomer dominates as indicated in the examples described above.

The dechlorination of fluorine-containing butanes according to this method is preferably carried out with zinc in a dechlorination solvent. Solvents useful for this purpose include the lower aliphatic alcohols such as methanol, ethanol or propanol, the carbitols, the cellosolves, benzyl alcohol, dioxane and mixtures of dioxane and glycerin. The dechlorination reaction is suitably carried out at moderate temperatures and preferably under reflux conditions to distill the dechlorinated product from the reaction mixture as it is formed. The immediate removal of the product makes it possible to dechlorinate a butane only partially where it contains at least four chlorine atoms. Other suitable dechlorinating metals may also be used such as magnesium.

Fluoro compounds containing halogens other than chlorine are prepared by treating a dechlorinated butane with the desired halogen. For example, the butane product of Example 5, CF -CFCI--CFCICF may be deehlorinated to yield perfluorobutene-Z which upon treatment with bromine yields the 2,3-dibromo derivative CF -CFBr-CFBr-CF with a boiling point of 950 C. (751 mm.) and a refractive index n 1.3574. This compound had an observed molecular weight of 361 (theoretical 359.9). Another example of this type of component is 2,3-dibromo-L4- m 10 dichloroperfluorobutane, CF Cl--CFBr-CFBrCFCl, prepared by partially dichlorinating to yield CF Cl-CF=CFCFCl and then brominating this olefin. The recultant bromine-containing butane, CF ClCFBrCFBrCF Cl, has a boiling point of 60- 65 C. (12 mm.) and a refractive index n 1.428.

The butanes, butenes, and butadienes prepared in accordance with the methods described herein are valuable for many purposes. Those butanes containing chlorine may be dichlorinated to yield butene or butadiene monomers for synthesising corrosion and heat resistant higher polymers. Polymerizations of the conjugated butadienes yield rubbery plastic materials. For example, the conjugated butadienes, notably hexafluorobutadiene-1,3, may be polymerized according to the methods disclosed in my copending application, Serial No. 10,912, filed February 25, 1948, now US. Patent No. 2,567,956, and in the copending application of Miller et al. Serial No. 773,292, filed September 10, 1947, now US. Patent No. 2,586,550. Lower molecular weight products formed from this compound, for example by the methods disclosed herein, and containing up to about 36 carbon atoms may be treated with fluorine or chlorine as described in my copending application Serial No. 601,387, filed June 25, 1945, now abandoned. Such treatment saturates the compound and provides liquids or grease-like materials which are suitable as heat exchange media, lubricants, solvents and the like having a high degree of chemical stability.

Since many embodiments might be made of the present invention and since many changes might be made in the embodiment described, it is to be understood that the foregoing decription is to be interpreted as illustrative only and not in a limiting sense.

I claim:

1. A method of preparing hexafluorobutadiene-1,3 which comprises reacting sym-dichlorodifluoroethylene with fluorine at a temperature of less than 10 C. to produce 1,2,3,4-tetrachloroperfluorobutane and dichlorinating at a temperature between about 50 C. and about 250 C. said butane to leave hexafluorobutadiene-1,3.

2. A method of preparing hexafluorobutadiene-1,3 which comprises reacting sym-dichlorodifluoroethylene with elemental fluorine at a temperature of less than 10 C. to produce 1,2,3,4-tetrachloroperfluorobutane and reacting at a temperature between about 50 C. and about 250 C. said butane with zinc in a dechlorinating solvent to dechlorinate said butane and leave hexafluorobutadiene-1,3.

3. A method for preparing hexafluorobutadiene-1,3 which comprises reacting sym-dichlorodifluoroethylene with elemental fluorine at a temperature of less than 10 C. to produce 1,2,3,4-tetrachloroperlluorobutane and reacting said butane with zinc at a temperature of between about 50 C. and about 250 C. in an aliphatic alcohol to dechlorinate said butane and leave hexafluorobutadione-1,3.

4. A method of preparing hexafluorobutadiene-1,3 which comprises dechlorinating with zinc 1,2,3,4-tetrachloroperfluorobutane dissolved in an aliphatic alcohol at a temperature between about C. and about 200 C.

References Cited in the file of this patent UNITED STATES PATENTS 924,304 Askenasy et al. June 8, 1906 2,377,297 Lamb et a1. May 29, 1945 2,399,024 Harmon Apr. 23, 1946 2,401,897 Benning et a1 June 11, 1946 2,590,433 Blum Mar. 25, 1952 2,628,987 Ruh Feb. 17, 1953 2,716,141 Miller Aug. 23, 1955 2,844,636 Haszeldine er a1. July 22, 1958 

1. A METHOD OF PREPARING HEXAFLUOROBUTADIENE-1,3 WHICH COMPRISES REACTING SYM-DICHLORODIFLUOROETHYLENE WITH FLUORINE AT A TEMPERATURE OF LESS THAN 10*C. TO PRODUCE 1,2,3,4-TETRACHLOROPERFLUOROBUTANE AND DICHLORINATING AT A TEMPERATURE BETWEEN ABOUT 50*C. AND ABOUT 250*C. SAID BUTANE TO LEAVE HEXAFLUOROBUTADIENE-1,3. 